Resin pulleys are commonly used as components of industrial machines or automobiles because they are light in weight and capable of lowering noises and lowering costs, compared to metallic pulleys. Among such resin pulleys, a pulley made of phenolic resin is more frequently used because it has advantages over a pulley made of thermosetting resin, typically of nylon that dimension accuracy is improved and deformation is less likely to occur.
A pulley made of phenolic resin is requested to have mechanical strength, dimension reliability, and thermal shock resistance. Also a pulley made of phenolic resin is requested to have characteristics appropriate for its fixing manner. When a pulley is fixed by using a bolt, the pulley is requested to have excellent stress relaxation from the view point of preventing the bolt from loosing. On the other hand, when a pulley is fixed by introducing an insert inside the pulley, a crack may occur in the vicinity of the insert due to a difference in thermal expansion between the insert and the resin. For this reason, an excellent thermal shock resistance is required. Thus in a pulley made of phenolic resin, it is necessary to achieve a good balance among a variety of required properties at a high-dimensional level.
Conventionally, a fixing method by introducing an insert into a pulley made of phenolic resin is often employed. In this case, an excellent thermal shock resistance is required as described above. For addressing this, a glass fiber is blended into a phenolic resin in a phenolic resin molding material for pulley in order to improve the thermal shock resistance, the mechanical strength and the dimension reliability. Patent document 1 describes mixing a phenolic resin, an elastomer, an organic fiber, a glass fiber, and a powder silica, thereby obtaining an effect of improving the heat shock resistance.
Patent document 1: Japanese Patent Application Laid-Open No. 2001-187958